A Pozzolan is a supplementary cementitious material that reacts with the calcium hydroxide in wet concrete to form a cementing compound. Some examples of Pozzolans are:
Blast Furnace Slag
Fly Ash is a waste powder produced from burning coal which improves pumpability/workability of concrete, reduce drying shrinkage cracking, increases sulfate resistance, decreases permeability, and increases concrete strength. Microsilica (or silica fume) is a bi-product of electronic semiconductor chip manufacturing which is about 100 times finer than cement. Microsilica when added to a concrete mix, produces very high concrete strengths and reduces permeability. Slag cement (or blast furnace slag) is a byproduct of iron manufacturing and when added to concrete, improves workability, increases strength, reduces permeability, and improves sulfate resistance.